The present invention relates to processing of physical media (e.g., blank printing stock, product packaging, catalogs, advertisements, etc.) to impart a machine-readable indicia (e.g., a plural-bit digital watermark) thereto.
Digital watermarking technology, a form of steganography, encompasses a great variety of techniques by which plural bits of digital data are hidden in some other object without leaving human-apparent evidence of alteration.
Most commonly, digital watermarking is applied to digital objects, such as digital image, video, and audio. In the case of images, slight changes can be made to local luminance or color values to effect the encoding. These changes can later be detected by a computer, and analyzed to discern the watermark information represented thereby.
Digital watermarking techniques can also be applied to traditional physical objects, including blank paper. Such blank media, however, presents certain challenges since there is no image that can serve as the carrier for the watermark signal.
The assignee""s U.S. Pat. 5,850,481 notes that the surface of a paper or other physical object can be textured with a pattern of micro-indentations to steganographically encode plural-bit information. The texturing is optically discernible, e.g., by a scanner, permitting the "Parenopenst" digital data to be decoded from scan data corresponding to the paper object.
In application Ser. No. 09/127,502, the present assignee taught various other arrangements by which blank media can be processed to encode a digital watermark. Some techniques employ very subtle printing, e.g., of fine lines or dots, which has the effect slightly tinting the media (e.g., a white media can be given a lightish-green cast). To the human observer the tinting appears uniform. Computer analysis of scan data from the media, however, reveals slight localized changes, permitting the multi-bit watermark payload to be discerned. Such printing can be by ink jet, dry offset, wet offset, xerography, etc.
Other techniques disclosed in the ""502 application extend the texturing techniques first set forth in the ""481 patent, e.g., by employing an intaglio press to texture the media as part of the printing process (either without ink, or with clear ink).
In one aspect, the present specification further develops and extends the techniques disclosed in the ""502 application.
For example, printable mediaxe2x80x94especially for security documents (e.g., banknotes) and identity documents (e.g., passports)xe2x80x94is increasingly fashioned from synthetic materials. Polymeric films, such as are available from UCB Films, PLC of Belgium, are one example. Such films may be clear and require opacification prior to use as substrates for security documents. The opacification can be effected by applying plural layers of ink or other material, e.g., by gravure or offet printing processes. (Suitable inks are available, e.g., from Sicpa Securink Corp. of Springfield, Va.) In addition to obscuring the transparency of the film, the inks applied through the printing process form a layer that is well suited to fine-line printing by traditional intaglio methods. Such an arrangement is more particularly detailed in laid-open PCT publication WO98/33658. That application is a pending U.S. counterpart application, now published as U.S. 2003/0003275, A1 which claims priority to Australian application 4847, filed Jan. 29, 1997.
In accordance with certain embodiments of the present invention, a machine readable indicia encoding plural bits (e.g., a digital watermark) is embedded as part of such an opacification process.
Other security documents employ plural substrates bound together in a laminate structure. The laminates variously include paper, polypropylene film, polyethelyne film, polyurethane film, metal film, inks, adhesives, optically-variable devices (e.g., holograms), and other materials. (See, e.g., U.S. Pat. Nos. 5,935,696 and 5,618,630.) Again, in accordance with embodiments of the present invention, plural-bit machine readable indicia can be incorporated in such structures.